This invention relates in general to post frame buildings and more particularly to a method of constructing such buildings and to an improved building resulting therefrom.
Post frame buildings, which evolved from the so-called pole barns, are used for a wide variety of commercial, industrial and agricultural purposes, for they are, compared to other types of construction, relatively easy and inexpensive to erect. In this regard, the typical post frame building has a series of wooden posts or columns along its perimeter, with these columns being set into the earth. The columns are tied together by horizontal members, called girts, and support wooden roof trusses which are joined together with purlins. Bracing is also normally incorporated into the structure. The trusses in turn support a light weight roofing, whereas the girts have a suitable siding material attached to them.
The typical construction sequence involves boring a series of 12 inch diameter holes around the perimeter for the building on four to ten foot centers. Each hole is about four feet deep and a precast concrete base or a dry mix is placed at its bottom. Next, the posts or columns are set into the holes which are then back filled to maintain the poles in a truly vertical position. Since many buildings require clearances as high as 18 to 20 feet, it is not uncommon to use solid wood columns as long as 24 feet. These columns, because they are set into the earth, must be treated with a wood preservative. While it is possible to cut the columns to the same length, it is virtually impossible to control the depth of the holes with any precision, particularly when there are slight variations in grade. As a consequence, a chalk line is usually struck along the upper ends of the columns to establish the elevation for the bearing surfaces on which the roof trusses will rest. Once this elevation is established, a workman either cuts a notch (FIG. 2) into the upper end of the column with a chain saw or else nails a bearing block (FIG. 3) to the side of the column to provide the bearing surface. In either case, the workman must manipulate tools high in the air without any nearby support to provide stability, other than the column itself. Often the result is a poorly configured or inaccurately positioned bearing surface. Thereafter, the roof trusses are installed and likewise the girts and purlins. Then, before the roofing is installed, the columns are cut off flush with the upper chords of trusses, but this is considerably easier than notching the columns or attaching bearing blocks to them, because the trusses and the connecting purlins provide locations where the workman can gain a foot hold or hand hold or otherwise brace himself.
In a somewhat different procedure the columns are of a laminated nature, usually consisting of three or more 2.times.6's or 2.times.8's arranged side-by-side. Moreover, the column is usually supplied in two sections--a lower section which is treated with a preservative and an upper section which is not--and at the joint between the sections the center piece of each section is offset vertically from the two side pieces so as to create a slip joint. This type of arrangement must likewise be leveled so that all columns possess the same height, and this leveling is accomplished by cutting the three pieces of each lower section so that the upper ends of corresponding pieces for all of the lower sections are at the same elevation. While the workman can make these cuts while standing at grade elevation, still three cuts must be made with a good deal of precision. Then the upper sections are fitted over the lower sections and the two sections are joined together with nails or truss plates at the slip joint that is so formed.
While columns of this nature are not quite as strong as solid wood columns, they are perhaps somewhat easier to construct and they need not be treated with preservative throughout. Even so, three cuts must be made with considerable precision on a vertical section, and the cuts in the two outer pieces of the section must be such that they do not weaken the center piece. This requires holding the saw in an awkward position and is time consuming. Furthermore, at the slip joint the individual pieces of the two sections abut at their ends, and under substantial loading the fibers of corresponding pieces in the upper and lower sections tend to intermesh, thereby causing the pieces to split at their ends. This compressive loading is most likely to occur as the result of excessive moments created by wind forces on the building.
To rigidify conventional post frame buildings, it is not uncommon to install knee bracing between the roof trusses and the columns on which they are supported, these braces being merely wood pieces extended at an angle between the trusses and columns. The installation of this type of knee bracing is difficult because it requires workmen to nail the bracing in place while working at considerable height. Also, the connections are highly variable.